A power distribution network line ice melting device and method based on low-dispersion electromagnetic switch

Abstract

The application provides a power distribution network line ice melting device and method based on a low-dispersity electromagnetic switch, comprising: an electromagnetic switch for controlling the switching in and out of a capacitor bank in a power distribution line; a resistance-capacitance oscillation circuit for interacting with the residual magnetism in an electromagnet in the electromagnetic switch body to generate an oscillation current and consume the oscillation current to reduce the dispersity of the closing of the electromagnetic switch; a super capacitor for discharging a field coil to realize the closing or opening action of the electromagnetic switch; a first control switch and a second control switch for the closing control and opening control of the electromagnetic switch respectively. The control strategy is to control the first electromagnetic switch and the second electromagnetic switch to be closed simultaneously at the intersection of the A-phase and B-phase sine alternating current, and to control the third electromagnetic switch to be closed at the first zero-crossing point of the C-phase. The application realizes the surge-free switching in control of the capacitor bank through the low-dispersity electromagnetic switch, and has the effects of simple structure, small size, low cost, high reliability and the ability to avoid large closing current.

Description

Technical Field

[0001] This invention relates to the field of power line de-icing technology, specifically to a distribution network line de-icing device and method based on a low-discreteness electromagnetic switch. Background Technology

[0002] In recent years, due to the spread of extreme weather around the world, problems such as increased weight, sagging, and even breakage of power lines caused by icing have become more frequent in winter. It is necessary to melt the ice on power lines to ensure the safe and stable operation of the power grid and avoid power outages.

[0003] Currently, in line de-icing technology, SVG (Static Var Compensator) de-icing utilizes a static var compensator (SVG) to heat up and melt the iced lines by outputting a controllable DC voltage. See also... Figure 1 In the SVG de-icing line, the H-bridge three-phase inverter is connected in parallel with the system through inductor L, and the magnitude and direction of the preset current are used as the conditions for closed-loop control. The magnitude and phase of the inverter terminal voltage U1 are controlled by pulse width modulation wave. The working state of SVG de-icing includes: (1) When the inverter terminal voltage U1 and the system voltage U2 are equal, the current output of SVG is 0; when the inverter terminal voltage U1 is greater than the system voltage U2, SVG outputs capacitive reactive current; when the inverter terminal voltage U1 is less than the system voltage U2, SVG outputs inductive reactive current. It can be seen that the reactive current output by SVG increases the total current of the line, causing the line to heat up and thus achieving the effect of melting the ice on the line. However, the existing SVG DC de-icing device is mainly composed of power electronic devices. Its control structure is complex and expensive. The initial investment and maintenance costs are relatively high, so it is not suitable for widespread promotion. Secondly, the existing SVG de-icing equipment is large in size and occupies a large area, which is not conducive to deployment in remote mountainous areas where freezing rain and icing are frequent. In addition, due to the large number of power electronic devices, the reliability of the devices may be reduced during long-distance transportation.

[0004] See Figure 2 If a relatively simple and low-cost reactive power compensation device FC is used for line de-icing, it is only necessary to control the capacitor C and reactor L in parallel with the system through the circuit breaker QF to generate capacitive reactive current, which can increase the total current of the line and thus achieve the de-icing effect through line heating. However, further analysis shows that according to the capacitor charging current formula:

[0005]

[0006] Where I is the peak value of the capacitor current, C is the capacitance value, dU is the difference between the system voltage and the initial voltage of the capacitor when the circuit is closed, and dt is the time required for the capacitor to reach the system voltage from the initial voltage.

[0007] As shown in the above formula, if the initial phase angle of circuit breaker QF is at the peak voltage, it will cause a very large inrush current. At the end of the distribution network, since the overcurrent setting of relay protection is usually small, the sudden connection of a large-capacity capacitor may cause the relay protection to malfunction and disconnect the line. Furthermore, a sudden large inrush current can also cause a voltage dip on the user side of the transmission line, which may damage normally operating power and electronic equipment, leading to serious economic losses.

[0008] Therefore, there is a need to design a simple, small-sized, low-cost, highly reliable ice-melting device and method for distribution network lines that can avoid large closing currents. Summary of the Invention

[0009] The present invention provides a distribution network line de-icing device and method based on a low discreteness electromagnetic switch, which is mainly used to solve the problems of complex structure, high cost, poor reliability and large closing current generated when the existing de-icing equipment is connected to the line. The device achieves the effects of simple structure, small size, low cost, high reliability and avoidance of large closing current.

[0010] The present invention achieves the above objectives through the following technical solutions:

[0011] A power distribution line de-icing device based on a low-discretion electromagnetic switch includes a first electromagnetic switch, a second electromagnetic switch, a third electromagnetic switch, and three sets of capacitor banks. The three sets of capacitor banks are respectively connected to phase A, phase B, and phase C of the power distribution line through the first electromagnetic switch, the second electromagnetic switch, and the third electromagnetic switch. Each electromagnetic switch includes an electromagnetic switch body and an electromagnetic control circuit, which are used to control the switching in and out of each capacitor bank in the power distribution line. The electromagnetic control circuit includes a RC oscillation circuit, a supercapacitor, and a control circuit. The RC oscillation circuit interacts with the residual magnetism in the electromagnet of the electromagnetic switch body to generate an oscillating current and consumes the oscillating current to reduce the dispersion of the electromagnetic switch closing. The supercapacitor is connected in parallel with the excitation coil of the electromagnet through the control circuit and is used to discharge the excitation coil to realize the closing or opening action of the electromagnetic switch. The control circuit includes a first control switch and a second control switch. The two ends of the supercapacitor are respectively connected to the excitation coil through the first control switch and the second control switch. The first control switch is used for closing control and opening control of the electromagnetic switch, respectively.

[0012] The control strategy of the first control switch among the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch is as follows: at the intersection of the sinusoidal alternating current of phase A and phase B, the first electromagnetic switch and the second electromagnetic switch are controlled to close simultaneously, and at the first zero crossing point of phase C, the third electromagnetic switch is controlled to close, so as to achieve inrush-free closing control.

[0013] A further embodiment is that the electromagnetic control circuit also includes a DC-DC boost circuit, the input terminal of which is connected to the battery output terminal in the switch cabinet, for inputting 48V DC power and converting the 48V DC power into 690V DC power for output to the supercapacitor.

[0014] A further approach is to use a float charging method to charge the supercapacitor using the DC-DC boost circuit.

[0015] A further option is that the DC-DC boost circuit adopts an isolated boost circuit with an output voltage accuracy of 0.1%.

[0016] A further embodiment is that the RC oscillation circuit includes a relay, a resistor, and a capacitor. One end of the resistor is connected to the first output terminal of the DC-DC boost circuit through the normally open contact of the relay, and the other end is connected to the second output terminal of the DC-DC boost circuit through the capacitor.

[0017] After the electromagnetic switch is opened, the relay is used to connect to the RC oscillation circuit by controlling its normally open contact to close. The capacitor is used to generate the oscillation current by exchanging energy with the residual magnetism in the electromagnet. The resistor is used to convert the oscillation current flowing through it into heat energy for consumption, thereby eliminating the residual magnetism in the electromagnet and reducing the discreteness of the electromagnetic switch closing.

[0018] A further embodiment is that both the first control switch and the second control switch are IGBT transistors, with their gates connected to a first control signal and a second control signal, respectively. The first control switch controls the transistor to conduct according to the first control signal to close the electromagnetic switch; the second control switch controls the transistor to conduct according to the second control signal to open the electromagnetic switch.

[0019] A further proposed solution is that the inherent closing times of the first electromagnetic switch, the second electromagnetic switch, and the third electromagnetic switch are respectively A S B S C S The first closing signal and the second closing signal of the first electromagnetic switch and the second electromagnetic switch are respectively A ahead of time. S B SThe timing is such that the potentials of phase A and phase B are equal when the circuit is closed; the third closing signal of the third electromagnetic switch is advanced by C. S The time is given so that when the circuit is closed, the phase voltage between phase C and phase B satisfies: V cb =V c -V b =0.5*V ab .

[0020] A method for de-icing distribution network lines based on a low-discreteness electromagnetic switch, applied to the aforementioned de-icing device for distribution network lines based on a low-discreteness electromagnetic switch, includes:

[0021] S1: Detect the inherent closing time A of the first electromagnetic switch, the second electromagnetic switch, and the third electromagnetic switch respectively. S B S C S .

[0022] S2: Start the de-icing operation and check the three-phase sinusoidal AC power in the power distribution line.

[0023] S3: At the next crossover point of the sinusoidal alternating current of phases A and B, respectively, advance phase A... S B S The system sends a first closing signal and a second closing signal to the first electromagnetic switch and the second electromagnetic switch at the specified time.

[0024] S4: At the next zero-crossing point of the C-phase sinusoidal alternating current, advance C... S The third closing signal was issued at the designated time.

[0025] S5: The first electromagnetic switch and the second electromagnetic switch are closed at the intersection point, and phases A and B are respectively connected to the capacitor bank. The third electromagnetic switch is closed at the zero-crossing point, and phase C is connected to the capacitor bank.

[0026] S6: The above three sets of capacitor banks send capacitive reactive current to the line, causing the line to heat up and melt ice.

[0027] Therefore, the present invention has the following beneficial effects:

[0028] 1. This invention utilizes a RC oscillation circuit to reduce the residual magnetism of the iron core to zero after each opening of the electromagnetic switch, thereby minimizing the dispersion of the switch's closing speed. Compared to traditional reactive power compensation devices (FC) used in circuit breakers or existing electromagnetic switches, this invention avoids the problems of energy loss due to excessive transmission links and the influence of mechanism movement speed leading to large dispersion. Furthermore, by leveraging the precision of the low opening and closing dispersion electromagnetic switch, capacitor banks are switched in phases at a favorable initial phase angle at equipotential conditions, achieving inrush-free capacitor bank switching control. This completely avoids problems such as relay protection malfunctions and voltage dips on the user side caused by large closing inrush currents.

[0029] 2. This invention uses a low-frequency discrete electromagnetic switch to achieve phase switching of capacitor banks, thereby carrying out de-icing operations. Compared with the traditional SVG de-icing solution, which has a complex structure, high cost, and poor reliability, this de-icing device has a simple structure, small size, and low cost. Moreover, the circuit design is relatively simple, which improves the reliability of the device and enables the popularization of de-icing devices for power distribution lines in different application environments.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an existing SVG ice-melting solution.

[0032] Figure 2 This is a schematic diagram of the existing reactive power compensation device FC ice melting scheme.

[0033] Figure 3 This is a schematic diagram of an existing electromagnetic switch circuit.

[0034] Figure 4 This is a schematic diagram showing the relationship between the magnetic field strength and the switching speed of an electromagnetic switch.

[0035] Figure 5 This is a schematic diagram of the electromagnetic switch circuit according to an embodiment of the present invention. Figure 1 .

[0036] Figure 6 This is a schematic diagram of the electromagnetic switch circuit according to an embodiment of the present invention. Figure 2 .

[0037] Figure 7 This is a flowchart of a distribution network line de-icing method based on a low-discreteness electromagnetic switch, according to an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] An embodiment of a distribution network line de-icing device based on a low-discretivity electromagnetic switch

[0040] This invention relates to a power distribution line de-icing device based on a low-discreteness electromagnetic switch, comprising a first electromagnetic switch, a second electromagnetic switch, a third electromagnetic switch, and three sets of capacitor banks. The three sets of capacitor banks are respectively connected to phases A, B, and C of the power distribution line via the first, second, and third electromagnetic switches. Each electromagnetic switch includes an electromagnetic switch body and an electromagnetic control circuit 40, used to control the switching in and out of each capacitor bank on the power distribution line. The electromagnetic control circuit 40 includes a RC oscillation circuit 20, a supercapacitor 30, and a control circuit 40. The RC oscillation circuit 20 is used for... The supercapacitor 30 interacts with the residual magnetism in the electromagnet of the electromagnetic switch body to generate an oscillating current, and consumes the oscillating current to reduce the dispersion of the electromagnetic switch closing. The supercapacitor 30 is connected in parallel with the excitation coil 50 of the electromagnet through the control circuit 40, and is used to discharge the excitation coil 50 to realize the closing or opening action of the electromagnetic switch. The control circuit 40 includes a first control switch and a second control switch. The two ends of the supercapacitor 30 are connected to the excitation coil 50 through the first control switch and the second control switch, respectively. The first control switch and the second control switch are used for closing control and opening control of the electromagnetic switch, respectively.

[0041] The control strategy of the first control switch among the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch is as follows: at the intersection of the sinusoidal alternating current of phase A and phase B, the first electromagnetic switch and the second electromagnetic switch are controlled to close simultaneously, and at the first zero crossing point of phase C, the third electromagnetic switch is controlled to close, so as to achieve inrush-free closing control.

[0042] Specifically, the electromagnetic switch body described in this embodiment includes a switch body, an electromagnet, a spring mechanism, and contacts. The switch body includes a stationary contact, a moving contact, and an insulating base, etc., for performing opening and closing actions. The electromagnet includes an iron core, a coil, and a movable iron plate, etc., for controlling the operation of the switch body through the electromagnetic control circuit 40. The spring mechanism is used to control the opening and closing of the moving contact when the electromagnet is attracted. The contacts are placed in the switch body and serve as conductive contacts to control the switch. The working process of the electromagnetic switch body is as follows: after the electromagnet is excited by the current output from the electromagnetic control circuit 40, it generates a magnetic field. The magnetic field acts on the iron core, pressing the moving contact against the stationary contact, closing the circuit, and realizing the closing of the electromagnetic switch; when the circuit current exceeds a set value, the contact iron plate is displaced, causing the moving contact to open, breaking the circuit, and realizing the opening of the electromagnetic switch.

[0043] The iron core is made of a semi-hard magnetic material, such as a cobalt-nickel-iron alloy.

[0044] Specifically, in this embodiment, when the electromagnetic switch is closed, the supercapacitor 30 discharges to the excitation coil 50 of the electromagnetic switch, generating magnetic flux in its core, which overcomes the spring force to close the circuit. At this time, the iron core, made of semi-hard magnetic material, becomes a permanent magnet after one excitation. When the electromagnetic switch is opened, the supercapacitor 30 discharges to the excitation coil 50 of the electromagnetic switch, demagnetizing its core, and the opening is achieved by the spring force.

[0045] Specifically, in this embodiment, the factors affecting the switching speed are the excitation voltage, the residual magnetism of the semi-hard magnetic material, and the mechanical force of the spring. The spring force exhibits negligible dispersion. The accuracy of the excitation voltage is ensured by the DC / DC boost circuit. An oscillation demagnetization circuit ensures that the residual magnetism of the semi-hard magnetic material returns to zero after each opening, thereby minimizing the dispersion of the switching speed during each closing action.

[0046] In this embodiment, the electromagnetic control circuit 40 further includes a DC-DC boost circuit 10. The input terminal of the DC-DC boost circuit 10 is connected to the battery output terminal in the switch cabinet to input 48V DC power and convert the 48V DC power into 690V DC power for output to the supercapacitor 30.

[0047] In this embodiment, the DC-DC boost circuit 10 uses a float charging method to charge the supercapacitor 30.

[0048] Specifically, in this embodiment, the DC-DC boost circuit 10 serves as a charging device for the supercapacitor 30 on the line, ensuring the voltage accuracy output to the excitation coil 50. The supercapacitor 30 can charge and discharge as the power line voltage fluctuates. When the capacitor bank capacity is small and the power line voltage is high, the supercapacitor 30 charges; when the capacitor bank capacity is large or the power supply is unexpectedly interrupted, the supercapacitor 30 discharges, sharing part or all of the output. It can be seen that the voltage of the supercapacitor 30 in the float charge state is generally constant. The small amount of current provided by the DC-DC boost circuit 10 from the power line compensates for the localized losses of the supercapacitor 30, ensuring it is always kept in a fully charged state without overcharging.

[0049] In this embodiment, the DC-DC boost circuit 10 adopts an isolated boost circuit with an output voltage accuracy of 0.1%.

[0050] It can be seen that the error between the actual value and the theoretical value of the output voltage of the DC-DC boost circuit 10 does not exceed 0.1% of the actual measured value. That is, the output voltage is 690V DC, and the difference between the actual voltage value and the theoretical value is 0.69V.

[0051] Specifically, in this embodiment, the DC-DC boost circuit 10 employs a bridge converter circuit, including a PWM pulse generation circuit, a full-bridge drive circuit, a transformer, and a synchronous rectification circuit. The PWM pulse generation circuit generates eight sets of PWM pulses, each sent to the gate of a MOSFET. The full-bridge drive circuit includes four MOSFETs forming a full bridge, each composed of two half-bridges. The two switching nodes of each half-bridge are connected to the primary side of the transformer. The synchronous rectification circuit uses four synchronous rectifier MOSFETs forming a full bridge. The secondary side of the transformer is connected to these synchronous rectifier MOSFETs. The output voltage is controlled and adjusted by adjusting the duty cycle of the primary-side full-bridge MOSFETs.

[0052] See Figure 6 Q1 and Q4 are simultaneously turned on as a diagonal pair of MOSFETs, and Q2 and Q3 are simultaneously turned on as another diagonal pair of MOSFETs. VPRI is the primary voltage of the transformer, IPRI is the primary current of the transformer, and Q5 and Q8, Q6 and Q7 are used for synchronous rectification on the secondary side.

[0053] Specifically, see this embodiment. Figure 3 For existing electromagnetic switches, since the materials used in the finished product are fixed, the influence of materials on the switching speed can be ignored. The actual factors affecting the switching speed are the excitation voltage and the residual magnetism of the iron core. According to PWM pulse width modulation control theory, for a DC / DC boost circuit, the duty cycle of the IGBT is positively correlated with its output voltage to obtain a constant excitation voltage. See [link to relevant documentation]. Figure 4 When the residual magnetism in the iron core is zero, the magnetic field strength H2 obtained by a constant excitation voltage corresponds to the switching speed S1. When the residual magnetism is H1, the magnetic field strength of the switch after applying a constant excitation voltage is H3, corresponding to the switching speed S2. However, in practical applications, because the residual magnetism is greatly affected by time and environment, H1 is a variable with an unknown value, and the switching speed S2 of the electromagnetic switch cannot be determined. Therefore, the opening and closing actions of existing electromagnetic switches have a large dispersion.

[0054] See Figure 5 In this embodiment, the RC oscillation circuit 20 includes a relay, a resistor, and a capacitor. One end of the resistor is connected to the first output terminal of the DC-DC boost circuit 10 through the normally open contact of the relay, and the other end is connected to the second output terminal of the DC-DC boost circuit 10 through the capacitor.

[0055] After the electromagnetic switch is opened, the relay is used to connect to the RC oscillation circuit 20 by controlling its normally open contact to close. The capacitor is used to generate the oscillation current by exchanging energy with the residual magnetism in the electromagnet. The resistor is used to convert the oscillation current flowing through it into heat energy for consumption, thereby eliminating the residual magnetism in the electromagnet and reducing the discreteness of the electromagnetic switch closing.

[0056] In this embodiment, both the first control switch and the second control switch are IGBT transistors, with their gates connected to a first control signal and a second control signal, respectively. The first control switch controls the transistor to conduct according to the first control signal to close the electromagnetic switch; the second control switch controls the transistor to conduct according to the second control signal to open the electromagnetic switch.

[0057] In this embodiment, the inherent closing times of the first electromagnetic switch, the second electromagnetic switch, and the third electromagnetic switch are respectively A S B S C S The first closing signal and the second closing signal of the first electromagnetic switch and the second electromagnetic switch are respectively A ahead of time. S B S The timing is such that the potentials of phase A and phase B are equal when the circuit is closed; the third closing signal of the third electromagnetic switch is advanced by C. S The time is given so that when the circuit is closed, the phase voltage between phase C and phase B satisfies: V cb =V c -V b =0.5*V ab .

[0058] An Example of a Method for De-icing Distribution Network Lines Based on Low Discreteness Electromagnetic Switches

[0059] See Figure 7 The present invention relates to a method for de-icing distribution network lines based on low-discreteness electromagnetic switches, which is applied to a de-icing device for distribution network lines based on low-discreteness electromagnetic switches, comprising:

[0060] S1: Detect the inherent closing time A of the first electromagnetic switch, the second electromagnetic switch, and the third electromagnetic switch respectively. S B S C S .

[0061] S2: Start the de-icing operation and check the three-phase sinusoidal AC power in the power distribution line.

[0062] S3: At the next crossover point of the sinusoidal alternating current of phases A and B, respectively, advance phase A... S B SThe system sends a first closing signal and a second closing signal to the first electromagnetic switch and the second electromagnetic switch at the specified time.

[0063] S4: At the next zero-crossing point of the C-phase sinusoidal alternating current, advance C... S The third closing signal was issued at the designated time.

[0064] S5: The first electromagnetic switch and the second electromagnetic switch are closed at the intersection point, and phases A and B are respectively connected to the capacitor bank. The third electromagnetic switch is closed at the zero-crossing point, and phase C is connected to the capacitor bank.

[0065] S6: The above three sets of capacitor banks send capacitive reactive current to the line, causing the line to heat up and melt ice.

[0066] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A power distribution network line de-icing device based on low-discreteness electromagnetic switch, characterized in that, The application relates to a power distribution network line ice melting device based on low-dispersion electromagnetic switches. The device comprises a first electromagnetic switch, a second electromagnetic switch, a third electromagnetic switch and three groups of capacitors, the three groups of capacitors are connected to A phase, B phase and C phase of a power distribution line through the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch respectively; the electromagnetic switches all comprise electromagnetic switch bodies and electromagnetic control circuits, and are used for controlling the switching in and out of the capacitors in the power distribution line; the electromagnetic control circuit comprises a resistance-capacitance oscillation circuit, a super capacitor and a control circuit, the resistance-capacitance oscillation circuit is used for interacting with residual magnetism in an electromagnet in the electromagnetic switch body to generate an oscillation current, and the oscillation current is consumed to reduce the dispersion of the closing of the electromagnetic switch; the super capacitor is connected in parallel with a field coil of the electromagnet through the control circuit, and is used for discharging the field coil to realize the closing or opening of the electromagnetic switch; the control circuit comprises a first control switch and a second control switch, two ends of the super capacitor are connected to the field coil through the first control switch and the second control switch respectively, and the first control switch and the second control switch are used for the closing control and opening control of the electromagnetic switch respectively. The control strategy of the first control switch in the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch is that the first electromagnetic switch and the second electromagnetic switch are controlled to be closed at the intersection point of A phase and B phase of a sine alternating current, and the third electromagnetic switch is controlled to be closed at the first zero point of C phase after that, so that the no-inrush current closing control is realized.

2. The power distribution network line ice melting device based on low-dispersion electromagnetic switches according to claim 1, wherein the electromagnetic control circuit further comprises a DC-DC voltage boosting circuit, an input end of the DC-DC voltage boosting circuit is connected with a battery output end in a switch cabinet, 48V direct current is input, and the 48V direct current is converted into 690V direct current and output to the super capacitor.

3. The power distribution network line ice melting device based on low-dispersion electromagnetic switches according to claim 2, wherein the DC-DC voltage boosting circuit charges the super capacitor in a floating mode.

4. The power distribution network line ice melting device based on low-dispersion electromagnetic switches according to claim 3, wherein the DC-DC voltage boosting circuit adopts an isolation type voltage boosting circuit, and the output voltage precision is 0.1%.

5. The power distribution network line ice melting device based on low-dispersion electromagnetic switches according to claim 3, wherein the resistance-capacitance oscillation circuit comprises a relay, a resistor and a capacitor, one end of the resistor is connected to a first output end of the DC-DC voltage boosting circuit through a normally open contact of the relay, and the other end of the resistor is connected to a second output end of the DC-DC voltage boosting circuit through the capacitor. ​ ​ ​ ​ After the electromagnetic switch is opened, the relay is used to access the resistance-capacitance oscillation circuit by controlling the normally open contact to be closed, the capacitor is used to exchange energy with the residual magnetism in the electromagnet to generate the oscillation current, and the resistor is used to convert the oscillation current flowing through it into heat energy for consumption, thereby eliminating the residual magnetism in the electromagnet to reduce the dispersion of the closing of the electromagnetic switch.

6. The low-dispersion electromagnetic switch-based power distribution network line ice-melting device according to claim 1, characterized in that: The first control switch and the second control switch are both IGBT transistors, the gates of which are connected to the first control signal and the second control signal respectively, the first control switch controls the transistor to be turned on according to the first control signal to realize the closing of the electromagnetic switch, and the second control switch controls the transistor to be turned on according to the second control signal to realize the opening of the electromagnetic switch.

7. The low-dispersion electromagnetic switch-based power distribution network line ice-melting device according to any one of claims 1-6, characterized in that: The inherent closing time of the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch is A S , B S , C S respectively, the first closing signal and the second closing signal of the first electromagnetic switch and the second electromagnetic switch are sent A S , B S in advance respectively, so that the potentials of phase A and phase B are equal when the first electromagnetic switch and the second electromagnetic switch are closed; the third closing signal of the third electromagnetic switch is sent C S in advance, so that the phase voltage between phase C and phase B when the third electromagnetic switch is closed satisfies: V cb = V c -V b = 0.5*V ab .

8. A method for de-icing power distribution network lines based on low-dispersion electromagnetic switches, characterized in that, The low-dispersion electromagnetic switch-based power distribution network line ice-melting device according to any one of claims 1-7 comprises: S1: detecting inherent closing time A of the first electromagnetic switch, the second electromagnetic switch and the third electromagnetic switch respectively S , B S , C S ; S2: Start ice-melting operation and detect three-phase sinusoidal alternating current in the power distribution line; S3: advance A S , B S time to send the first closing signal, the second closing signal to the first electromagnetic switch, the second electromagnetic switch; S4: advance C at the next zero crossing of the C-phase sinusoidal AC S time to issue a third close signal; S5: The first electromagnetic switch and the second electromagnetic switch are closed at the intersection point, the A phase and the B phase are respectively connected to the capacitor bank, and the third electromagnetic switch is closed at the zero-crossing point, and the C phase is connected to the capacitor bank; S6: The three groups of capacitors emit capacitive reactive current to the line to heat the line and melt ice.

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